The present invention relates to cameras.
The present invention relates to single lens reflex cameras of the type where light is measured after travelling through the objective of the camera.
Such internal light measurement is advantageous as compared with external light measurement because on the one hand the deviation of the actual photographing angle of the objective from the angle of exposure which would be constant for an external light-measuring system can be eliminated, while on the other hand it is easy to determine a proper exposure multiple in order to compensate for a variation of the F-number due to an increase in advance of the objective for photographing at a short distance as well as due to a reduction in light intensity which occurs due to use of a filter or an attachment lens.
For the above reasons, internal light-measuring systems known as TTL or through-the-lens systems, has dominated the field of photographic cameras, particularly of the single-lens reflex type and many photographic cameras which utilize such an internal exposure system in connection with automatic exposure controls have been recently proposed.
It is, however, required that the so-called TTL system store information with respect to the object to be photographed, this information being obtained immediately before a mirror of the camera swings up from a viewing position to an exposure position, inasmuch as the light which comes from the object which is to be photographed is prevented from reaching the light-measuring structure of the camera when the mirror is displaced beyond the optical axis of the objective so as to enable an exposure to be made.
Moreover, it is common to measure the light when the diaphragm provides a fully open aperture, so that under these conditions the information which is stored is obtained prior to regulation of the diaphragm to provide the aperture required for film exposure. The operations in connection with storing this information is usually effected in connection with operation of the diaphragm mechanism and the mirror mechanism in such a way that the information with respect to the object which is to be photographed is stored just prior to actual film exposure, these operations usually being carried out automatically.
However, under certain photographing conditions such as when compensation is made for back-lighting or counter light, or when a bulb exposure or a time exposure are made, with the mirror swung up to the exposure position, the information with respect to the object which is to be photographed must preliminarily be stored, and this latter operation must be carried out manually. Various mechanisms for achieving such manual memory operations have already been proposed. Such mechanisms conventionally provide for operations which are independent of the automatic memory operation which is operatively associated with the diaphragm-controlling mechanism and mirror-controlling mechanism. Where there is an automatic exposure control for controlling an electrically-operated shutter, for example, there have been provided two memory switches so that the information with respect to the object to be photographed may be converted into the corresponding electrical quantity and stored in a memory capacitor by one or the other of the switches, one of these switches being automatically operated and the other one being manually operated. Such structure has lead to complications and a reduction in accuracy as well as a reduction in the liability of the operation. Thus, a leakage current will occur at each of the switching regions resulting in a variation in the voltage of a memory capacitor and therefore producing an error in the stored value.